Halogenated organic compounds are well known compounds and are used in a wide variety of applications as industrial chemical reactants, pesticides, dry cleaning solvents, electrical insulators and heat-exchange fluids. There are suspicions and a growing body of evidence that certain halogenated organic compounds may cause public health problems. As a result, federal regulations have been promulgated to control the use and level of exposure of the general public to halogenated organic compounds. Although certain halogenated organic compounds such as polychlorinated biphenyls have been widely used, they are now considered to be hazardous and their manufacture and use have been discontinued.
As indicated above, halogenated organic compounds are widely used in industry. Numerous methods exist to dispose of halogenated organic compounds and to dehalogenate the halogenated organic compounds to less toxic materials. For polychlorinated biphenyls, the only disposal procedure utilized to any degree at present is incineration at high temperature. However, extremely high temperatures must be used in this method to completely combust the higher chlorinated polychlorinated biphenyls and, unfortunately, these high temperature conditions may result in the formation of even more toxic dioxins.
Methods to dechlorinate polychlorinated biphenyls are known and they include reaction of hydroxides of alkali and alkaline earth metals with the polychlorinated biphenyls and organic solvents and the solvents are distilled off (see U.S. Pat. No. 4,477,354), reaction of the polychlorinated biphenyls with sodium naphthalimide generated in situ in ether-type solvents (see U.S. Pat. No. 4,326,090), reaction of the polychlorinated biphenyls with alkali metal hydroxides in polyglycol or polyglycol monoalkyl ethers (see U.S. Pat. No. 4,400,552), reaction of the polychlorinated biphenyls with nickel arylphosphine halide (see U.S. Pat. No. 4,400,566), reaction of the polychlorinated biphenyls with alkali mercaptides (see U.S. Pat. No. 4,410,422), reaction of the polychlorinated biphenyls with molten aluminum (see U.S. Pat. No. 4,469,661) and reaction of polychlorinated biphenyls with liquid sodium (see U.S. Pat. No. 4,465,590).
A review of the above methods demonstrates that the processes involved are generally useful in removing the halogens from halogenated organic compounds but that the chemical reactions require the use of hazardous materials or complicated reaction schemes.
The processes as described above are in general used to achieve dechlorination once the chlorinated organic compound has been isolated or separated from other materials. Known isolation or separation efforts to obtain the chlorinated organic materials include a solvent vapor extraction process to remove polychlorinated biphenyls from an electrical apparatus (see U.S. Pat. No. 4,483,717), use of a hot turbulent gas to remove polychlorinated biphenyls from contaminated sludges (see U.S. Pat. No. 4,402,274) and a method of solvent-extraction and degradation of polychlorinated biphenyls from contaminated oils (see U.S. Pat. No. 4,477,354). It is also known that polychlorinated biphenyls can be removed from waste oils and contaminated soils by extraction with solvents such as N,N-dimethylformamide (hereinafter dimethyl formamide or more simply "DMF") or water/kerosene mixtures as described in C. W. Haucher et al, NTIS DEA5002-619/LR (Nov. 1, 1984). It is easily recognized by those skilled in the art that these methods to isolate or separate polychlorinated biphenyls have general utility in isolating or separating halogenating organic compounds, but they are costly and their effectiveness is limited due to the large volumes of solvents required to maintain extraction efficiencies or the need for generating significant volumes of high temperature gas.
An electrochemical reaction for removal of chlorine atoms from organic compounds is disclosed in Kaabak et al, J. Org. Chem. USSR, 3: 1 (1967). The disclosure is of a chemical reaction between a reagent and a halogenated organic compound prior to electrolysis, this initial reaction providing a charge-carrying species for the electrolysis. Halogen removal by direct electron transfer from a cathode in a halogenated organic compound reduction is described in Feoktistov, Chap. VII, Organic Electrochemistry, M. M. Baizer and H. Lund, Eds., Marcell Dekker, New York (1983). Radical anion catalyst-based dehalogenation is also described as a method for removing a halogen from an organic halogenated compound in T. F. Connors and J. F. Rusling, J. Electrochem. Soc., 130: 1120 (1983). However, even though different methods of halogen removal from halogenated organic compounds are disclosed above or extraction processes to remove such are known, the methods identified above are hazardous, complex and expensive.